DE69204884T2 - Receiving element for dye transfer by thermal sublimation to produce a printed copy of an image for medical diagnostics. - Google Patents

Description

1. Field of the invention

The present invention relates to dye image-receiving elements for use in dye sublimation thermal transfer, in particular to dye image-receiving elements for use in accordance with a method of obtaining a printed copy of a medical diagnostic image by dye sublimation thermal transfer.

2. General state of the art

Dye sublimation thermal transfer, also referred to as dye diffusion thermal transfer, is a recording process in which a dye donor element provided with a dye layer containing sublimable dyes that can be transferred under the influence of heat is brought into contact with a receiver sheet and is selectively heated in accordance with a pattern information signal by means of a thermal print head provided with a plurality of heat-generating resistors arranged next to one another, whereby dye from the selectively heated areas of the dye donor element is transferred to the receiver sheet and forms a pattern on the latter, the shape and density of which corresponds to the pattern and the intensity of the heat acting on the dye donor element.

A dye-donor element to be used in dye sublimation thermal transfer generally comprises a very thin support, e.g. a polyester support, covered on one side with a dye layer containing the printing inks. Generally, an adhesive layer or substrate layer is provided between the support and the dye layer. Usually, the opposite side is covered with a lubricant layer which provides a lubricious surface along which the thermal print head can be guided without suffering abrasion. An adhesive layer may be provided between the support and the lubricant layer.

A dye-image receiving element for use Dye sublimation thermal transfer generally includes a carrier, eg paper or a transparent film, which is coated with a dye image receiving layer into which the dye can diffuse more easily. An adhesive layer can be provided between the carrier and the receiving layer. A separate separating layer can also be provided on the receiving layer to make it easier to separate the receiving element from the donor element after the transfer has taken place. A back coating can also be provided on the back of the carrier, ie the side opposite the receiving layer side, in order to improve the feeding of individual sheets from a stack of sheets or to provide the sheet with an antistatic treatment.

The dye layer may be a single-color dye layer or it may contain successive, repeating areas of different colored dyes, such as cyan, magenta, yellow and possibly black. If a dye donor element containing dyes corresponding to three or more primary colors is used, a multi-color image can be obtained by carrying out the dye transfer process steps sequentially for each color.

Dye sublimation thermal transfer printing can be used, among other things, to produce printed copies of images for medical diagnostics. Although it is possible to produce such a printed copy on a reflective substrate such as paper, most applications involve producing printed copies on slides. Depending on the application, these printed copies can be single-colour, in particular single-colour black, or multi-colour.

Printed copies of images for medical diagnostics produced on slides are read by a light source in front of a light box. The practical circumstances under which the images are actually read by the observers play an important role in accurately assessing the diagnostic data recorded in the printed copy.

When viewing images produced on conventional dye-sublimation slides in front of a light box, bright light emanating from around the printed copy impairs the observer's optical perception and therefore the observer's interpretation. In addition, transparent film borders adjacent to the image cause glare, which reduces the eye's ability to evaluate the diagnostic information contained in the image.

3. Brief description of the invention.

The object of the present invention is therefore to provide a dye thermal transfer printing process for obtaining a printed copy of a medical diagnostic image on a slide and a transparent receiver element to be used in accordance with this process, which do not have the disadvantages mentioned above.

According to the invention, a dye image receiving element is now provided which is printed by means of a dye sublimation thermal transfer, the dye image receiving element comprising a transparent carrier and thereon a transparent dye image receiving layer containing transferred dye images, characterized in that the dye image receiving element is provided with black borders which surround the image area(s).

When medical diagnostic images printed on receiver elements according to the invention are viewed on a light box, reflection and glare are virtually eliminated and details in the denser areas can be better assessed by masking surrounding areas.

4. Detailed description of the drawings

Figure 1 and Figure 2 each show a plan view of the receiver element embodying the present invention.

5. Detailed description of the invention.

In one embodiment of the present invention, the black borders are provided exclusively along the edges and margins of the receiver element and thus surround the image area of only one image when only one image is reproduced on the receiver element, as shown in Figure 1. In another embodiment of the present invention, black borders are provided not only along the edges and margins of the receiver element, but also at different distances within the plane of the receiver element and thus surround several image areas when a number of images are reproduced on the receiver element, as shown in Figure 2.

The black edges surrounding the image area(s) of the receiver element according to the invention preferably have a high optical density of at least 2. The density of these edges is measured in transmitted light using a Macbeth TR 924 densitometer equipped with a visual filter.

The black seams on the receiver element according to the invention can be produced in various ways.

During manufacture of the image-receiving element of the invention, the seams can be implemented by printing on either the back or the receiving side of the (uncoated) support of the receiving element. Printing can be done by offset printing, gravure printing, screen printing, aniline printing, electrophotographic or ionographic printing using conventional black inks. However, printing can also be done after the support has been coated with at least one of the layers generally included in dye-sublimation thermal transfer receiving elements (eg receiving layer, release layer on the receiving layer, backing layer or adhesive layer provided between the carrier and any of the above layers).

These seams can be made before or after cutting the receiver material into sheets.

The image receiving element according to the invention can also be provided with black seams during transfer printing of the receiving element. This is made possible by the use of a black dye donor element or a black dye donor area which contains a mixture of sublimable dyes and whose printing area is larger than the image area of the receiving element. For black-colored images, this black dye donor element or dye donor area can be the same dye donor element or dye donor area used to print the image and the black seams can be produced simultaneously with the image by sublimation transfer printing. The seams can also be produced on the receiving element by using a special dye donor element with a separate area containing black material (for example carbon black) in a wax layer by thermal transfer wax printing.

The image receptor element can be provided with black borders during transfer printing by using separate thermal heads for transfer printing the black borders. The advantage of using separate thermal heads instead of one thermal head for printing the black borders and the image(s) is that the image(s) can be printed with a smaller thermal head; large-sized thermal heads have a significant voltage drop.

To protect the resulting medical diagnostic image, the receiver element can be laminated with a transparent cover film after transfer printing (such cover films are described, for example, in EP 178332, EP 305922, EP 273347, EP 394460 and JP 01/237193). Such a cover film is used to improve the scratch resistance and light resistance of the transferred dye image obtained in this way and also to prevent the migration of the transferred dyes out of the receiving layer. The receiving element can also be provided with black seams after transfer printing by providing the cover film with which the receiving element is to be laminated after transfer printing with black seams.

With the help of the seams, if they are made before the sublimation transfer, it is not only possible to avoid unwanted glare, but also to bring the image receptor element into the exact desired position during the transfer printing. For this purpose, they can be equipped with detection marks.

The dye-receiving layer of the receiver element according to the invention can contain, as a binder, which must be transparent, for example a polycarbonate, a polyurethane, a polyester, a polyamide, polyvinyl chloride, polystyrene-acrylonitrile copolymer, polycaprolactone or mixtures thereof. Suitable dye-receiving layers have been described, for example, in EP 133011, EP 133012, EP 144247, EP 227094 and EP 228066. The dye-receiving layer can also contain a hardened binder such as the heat-hardened product of vinyl chloride-vinyl acetate-vinyl alcohol copolymer and polyisocyanate.

The total amount of binder used in the dye-receiving layer according to the invention is between 25 and 95 percent by weight, preferably between 50 and 80 percent by weight.

The dye-receiving element according to the invention can contain a release agent to improve the release properties with respect to the donor element. Suitable release agents are solid waxes such as polyethylene wax, amide wax and Teflon powder; fluorine-based and phosphate ester-based surfactants; and paraffin-based, silicone-based and fluorine-based oils. Silicone oils are preferred. in particular reactive silicone oils (such as hydroxyl-modified polydimethylsiloxane, e.g. TEGOMER HSI 2111, available from Goldschmidt), as well as silicone-containing copolymers such as polysiloxane-polyether copolymers and block copolymers (e.g. TEGOGLIDE, available from Goldschmidt, and SILWET, available from Union Carbide).

High-boiling organic solvents or thermal solvents or plasticizers can also be mixed into the image receiving layer, namely as substances that can absorb or dissolve the dyes or as diffusion accelerators for the dyes. Suitable high-boiling organic solvents and thermal solvents of this type include the compounds known from JP 62/174754, JP 62/245253, JP 61/209444, JP 61/200538, JP 62/8145, JP 62/9348, JP 62/30247 and JP 62/136646.

Also, to further improve the lightfastness of the transferred image, one or two or more types of additives such as UV absorbers, light stabilizers and antioxidants may optionally be added. The amounts of these UV absorbers and light stabilizers are preferably 0.05 to 10 parts by weight and 0.5 to 15 parts by weight, respectively, per 100 parts of the resin constituting the receiving layer.

The dye-receiving layer according to the invention preferably has a total thickness of 0.5 to 50 µm, particularly preferably of 2.5 to 10 µm.

If a cover layer containing a release agent of the type described above is provided on the receiving layer, the thickness of such a cover layer is preferably 0.01 to 5 µm, in particular 0.05 to 2 µm.

A transparent film or sheet made of various plastics such as polyethylene terephthalate, polyolefin, polyvinyl chloride, polystyrene, polycarbonate, polyethersulfone, polyimide, cellulose ester or polyvinyl alcohol acetate copolymer is used as a carrier for the receiver sheet. Blue-colored Polyethylene terephthalate film may be used as long as it remains transparent, transparent being defined as the property of allowing light to pass through without significant scattering. In general, the support has a thickness of at least 100 µm so that the printed copy can be easily placed on a light box. The thickness of the support is preferably in the range of 120 to 200 µm, more preferably in the range of 160 to 190 µm, most preferably between 170 and 180 µm.

The adhesion of a coating composition to the carrier material can be improved by providing a substrate layer between the carrier material and the coating layer (e.g. the receiving layer and/or the backing layer). Particularly preferred as substrate layers for polyethylene terephthalate carriers are substrate layers based on vinylidene chloride copolymers, as described in GB 1234755.

The image-receiving element according to the invention can also have at least one intermediate layer between the support and the image-receiving layer. Depending on the material from which they are formed, the intermediate layers can function as support layers, porous layers (as long as they remain transparent) or dye diffusion-preventing layers, or perform two or more of these functions, but can also serve as an adhesive, depending on the particular use.

The material constituting the intermediate layer can contain, for example, a urethane resin, an acrylic resin, an ethylenic resin, a butadiene rubber or an epoxy resin. The thickness of the intermediate layer is preferably 1 to 20 µm.

Dye diffusion-preventing layers are layers which prevent the dye from diffusing into the support. The binders used to form these layers can be water-soluble or soluble in organic solvents, but the use of water-soluble binders is preferred, with gelatin being particularly is attractive.

Porous layers are layers that prevent the diffusion of the heat supplied at the time of thermal transfer from the image receiving layer into the carrier in order to ensure that the heat supplied is used efficiently and to prevent any deformation of the carrier.

A transparent back coating may be provided on the side of the support opposite the image receiving layer side. This back coating may contain a matting agent as described in EP-A-0543.

Furthermore, the image receiving sheet can have a transparent sliding layer provided on the back surface of the film carrier. The material for the sliding layer can comprise methacrylate resins such as methyl methacrylate etc. or corresponding acrylate resins, vinyl resins such as vinyl chloride-vinyl acetate copolymers.

The front or rear surface of the image receiving element according to the invention can also be subjected to an antistatic treatment. Such an antistatic treatment can be carried out by incorporating an antistatic agent, for example in the image receiving layer, or can consist of an antistatic layer applied to the image receiving surface or inserted under it. The rear surface can also be subjected to a similar treatment. Such a treatment allows the image receiving sheets to slide easily against one another and also results in no dust being able to adhere to the image receiving sheet.

Furthermore, the receiver element can have a notch to distinguish the receiver layer side from the back coating side and be provided with rounded edges.

A dye-donor element to be used in accordance with dye-sublimation thermal transfer in conjunction with the present receiving element usually contains a very thin carrier, e.g. a polyester carrier, the one side is covered with a dye layer containing the printing inks. Usually an adhesive layer or substrate layer is provided between the carrier and the dye layer. Normally the opposite side is covered with a lubricant layer which provides a slippery surface along which the thermal print head can be guided without suffering abrasion. An adhesive layer can be provided between the carrier and the lubricant layer.

The dye layer may be a single-color dye layer or it may contain successive, repeating areas of different colored dyes, such as cyan, magenta, yellow and possibly black. If a dye donor element containing dyes corresponding to three or more primary colors is used, a multi-color image can be obtained by carrying out the dye transfer process steps sequentially for each color.

The dye layer of such a dye sublimation thermal transfer donor element is preferably formed by adding the dyes, polymeric binder and other optional components to a suitable solvent or solvent mixture, dissolving or dispersing the components to form a coating composition which is then applied to a support which may first have been provided with an adhesive layer or substrate layer and then dried.

The dye layer thus formed has a thickness of about 0.2 to 5.0 µm, preferably 0.4 to 2.0 µm, and the ratio of dye to binder is between 9:1 and 1:3 by weight, preferably between 2:1 and 1:2 by weight.

Suitable polymeric binders are: cellulose derivatives such as ethyl cellulose, hydroxyethyl cellulose, ethyl hydroxyethyl cellulose, hydroxypropyl cellulose, methyl cellulose, nitrocellulose, cellulose acetate formate, Cellulose acetate hydrogen phthalate, cellulose acetate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate pentanoate, cellulose acetate benzoate, cellulose triacetate; resins and derivatives of the vinyl type such as polyvinyl alcohol, polyvinyl acetate, polyvinyl butyral, polyvinyl butyral-vinyl acetal-vinyl alcohol copolymer, polyvinyl pyrrolidone, polyvinyl acetoacetal, polyacrylamide; polymers and copolymers derived from acrylates and acrylate derivatives such as polyacrylic acid, polymethyl methacrylate and styrene-acrylate copolymers; polyester resins; polycarbonates such as a polycarbonate derived from 2,2-bis-(4-hydroxyphenyl)propane; styrene-acrylonitrile copolymer; polysulfones, polyphenylene oxide; organosilicone such as polysiloxanes; epoxy resins and natural resins such as gum arabic. Cellulose acetate butyrate or styrene-acrylonitrile (butadiene) copolymer is preferably used as a binder for the dye layer.

Any dye can be used in such a dye layer, provided that it can be readily transferred to the dye image receiving layer of the receiver sheet by the action of heat.

Typical and specific examples of dyes to be used in dye sublimation thermal transfer are described, for example, in European patent application No. 90203014.7, EP 209990, EP 209991, EP 216483, EP 218397, EP 227095, EP 227096, EP 229374, EP 235939, EP 247737, EP 257577, EP 257580, EP 258856, EP 279330, EP 279467, EP 285665, EP 400706, EP 432313, EP 432314, EP 432829, EP 453020, US 4743582, US 4753922, US 4753923, US 4757046, US 4769360, US 4771035, JP 84/78894, JP 84/78895, JP 84/78896, JP 84/227490, JP 84/227948, JP 85/27594, JP 85/30391, JP 85/229787, JP 85/229789, Jp 85/229790, JP 85/229791, JP 85/229792, JP 85/229793, JP 85/229795, JP 86/41596, JP 86/268493, JP 86/268494, JP 86/268495 and JP 86/284489.

The coating layer may also contain other additives such as hardeners, preservatives, organic or inorganic fine grains, dispersants, antistatic agents, antifoam agents, viscosity regulators, etc., which, along with other ingredients, are described in more detail in EP 133011, EP 133012, EP 111004 and EP 279467.

Any material can be used as the support for the dye-donor element, provided that it is dimensionally stable and can withstand the temperatures used, up to 400°C for up to 20 msec, and yet is thin enough to allow heat applied to one side to pass through to the dye on the other side to effect transfer to the receiver sheet within such short periods of time, typically 1 to 10 msec. Such materials include polyesters such as polyethylene terephthalate, polyamides, polyacrylates, polycarbonates, cellulose esters, fluorinated polymers, polyethers, polyacetals, polyolefins, polyimides, glassine paper and capacitor paper. A polyethylene terephthalate support is preferred. Generally, the support has a thickness of 2 to 30 µm. Optionally, the support may also be coated with an adhesive layer or substrate layer.

The dye layer of the dye donor element can be applied to the support or printed using a printing technique, such as a gravure printing process.

The dye-donor element may also have a dye barrier layer comprising a hydrophilic polymer inserted between the support and the dye layer to improve dye transfer densities by preventing transfer of dye in the wrong direction, towards the support. The dye barrier layer may comprise any hydrophilic material suitable for the intended purpose. In general, good results are obtained with gelatin, polyacrylamide, polyisopropylacrylamide, butyl methacrylate grafted gelatin, ethyl methacrylate grafted gelatin, ethyl acrylate grafted gelatin, cellulose monoacetate, methylcellulose, polyvinyl alcohol, polyethyleneimine, polyacrylic acid, a mixture of polyvinyl alcohol and Polyvinyl acetate, a mixture of polyvinyl alcohol and polyacrylic acid or a mixture of cellulose monoacetate and polyacrylic acid. Suitable dye barrier layers have been described in eg EP 227091 and EP 228065. Certain hydrophilic polymers, eg those described in EP 227091, also exhibit sufficient adhesion to the support and dye layer, thereby eliminating the need for a separate adhesive or substrate layer. These certain hydrophilic polymers used in a single layer in the donor element thus perform a dual function and are therefore referred to as dye barrier/substrate layers.

Preferably, the back of the dye donor element can be coated with a lubricant layer to prevent the print head from sticking to the dye donor element. Such a lubricant layer would contain a lubricant medium such as a surfactant, a liquid lubricant, a solid lubricant or mixtures thereof, optionally with a polymeric binder. The surfactants can be any of those known in the art, such as carboxylates, sulfonates, phosphates, aliphatic amine salts, aliphatic quaternary ammonium salts, polyoxyethylene alkyl ethers, polyethylene glycol fatty acid esters, aliphatic fluoroalkyl C2-C20 acids. Examples of liquid lubricants include silicone oils, synthetic oils, saturated hydrocarbons and glycols. Examples of solid lubricants include various higher alcohols such as stearyl alcohol, fatty acids and fatty acid esters. Suitable lubricant layers are described, for example, in EP 138483, EP 227090, US 4567113, US 4572860 and US 4717711. Preferably, the lubricant layer contains a styrene-acrylonitrile copolymer or a styrene-acrylonitrile-butadiene copolymer or a cellulose ester or a polycarbonate derived from 2,2-bis-(4-hydroxyphenyl)propane as a binder and a polysiloxane-polyether copolymer or polytetrafluoroethylene as a lubricant in an amount of 0.1 to 10 percent by weight of the binder (mixture).

The dye layer of the dye donor element can also contain a release agent that facilitates the separation of the dye donor element from the dye acceptor element after transfer. The release agents can also be applied in a separate layer to at least part of the dye layer. Solid waxes, fluorine- or phosphate-containing surfactants and silicone oils are used as release agents. Suitable release agents are described, for example, in EP 133012, JP 85/19138 and EP 227092.

The ink receiving elements according to the invention are used to form a dye transfer image. In such a process, the dye layer of the donor element is placed against the dye receiving layer of the receiver sheet so that their surfaces touch, whereupon imagewise heating takes place from the back of the donor element. The transfer of the dye takes place by heating for several milliseconds to a temperature of 400°C.

If the process is carried out for only a single color, a single color dye transfer image is obtained. A multi-color image can be obtained by using a donor element containing three or more primary color dyes and sequentially performing the above-described process steps for each color. This layered arrangement of donor element and receiver sheet is formed three times within the period during which heat is applied via the thermal print head. After the first dye is transferred, the elements are released from each other. A second dye donor element (or another area of the donor element with a different dye area) is then brought into register with the dye receiver element and the process is repeated. The third color and optionally additional colors are obtained in the same way.

In addition to thermal heads, laser light, infrared flashes or heated pens. Thermal print heads are commercially available for transferring dye from the donor element to the receiver sheet. When laser light is used, the dye layer or another layer of the dye element must contain a compound that absorbs the light emitted by the laser and converts it into heat, eg carbon black.

The carrier of the dye donor element can also be an electrically poorly conductive ribbon, which consists, for example, of a multi-layer system of carbon-loaded polycarbonate coated with a thin aluminum film. Current is introduced into the poorly conductive ribbon by electrically charging a print head electrode, which leads to highly localized heating of the ribbon under the relevant electrode. The fact that the heat is generated directly in the poorly conductive ribbon and that the ribbon is thus heated provides an inherent advantage of the technology using a combination of poorly conductive ribbon and electrode head over thermal head technology, where the various elements of the thermal head must heat up and cool down before the head can move on to the next printing position.

The receiver element according to the invention is used for producing printed copies, in particular black and white printed copies of images for medical diagnostics, in particular in ultrasound, C-arm surgery and nuclear medicine applications.

The following examples may further explain the invention without, however, limiting its scope of protection.

EXAMPLE 1

A transparent polyethylene terephthalate support with a thickness of 175 µm was provided with a conventional image receiving layer on one side and with an antistatic layer on the other side.

On this antistatic layer, black seams were applied in a shape as shown in Figure 1. These black borders were printed by gravure printing. The printing solution contained: 50 g of magenta dye I, 30 g of cyan dye II, 25 g of yellow dye III and 50 g of binder (Luran 388S, supplied by BASF) in methyl ethyl ketone (the total weight of the solution was 1000 g). Dye I Dye II Dye III

The density of the black fringes thus obtained, measured with a Macbeth densitometer type TR924 behind a visual filter, was greater than 3. Minor fluctuations in density were barely perceptible; the visual impression obtained from the black fringes was uniformly black and they shielded unwanted light.

EXAMPLE 2

A transparent polyethylene terephthalate support with a thickness of 175 µm was provided with a conventional image receiving layer on one side and with an antistatic layer on the other side.

On this antistatic layer, black seams were produced in a form such as that shown in Figure 1. The printing of these black seams was carried out by offset printing using a SUPERMASTER SPP type printing plate supplied by Agfa-Gevaert and a GT046 type offset printing machine supplied by from Heidelberg. SONOPLAST VS494, supplied by Vanson, was used as the printing ink and ROTAMATIC, supplied by CP Bourg, was used as the fountain solution.

The black seams thus obtained had visual densities above 1.2 (measured with a Macbeth densitometer type TR924).

Claims (10)

1. Dye-image-receiving element which is printed by means of a dye-sublimation thermal transfer, with a transparent support and on the same a dye-image-receiving layer containing transparent, transferred dye images, characterized in that the dye-image-receiving element is provided with black borders which surround the image area(s). 2. A dye-image receiving element according to claim 1, wherein the black seams are provided along the edges and margins of the receiving element. 3. A dye-image receiving element according to claim 2, wherein further black seams are provided at different distances within the plane of the receiving element. 4. Dye-image-receiving element according to one of the preceding claims, wherein the black fringes have an optical density of at least 2. 5. A dye-image receiving element according to any one of claims 1 to 4, wherein the black seams are produced by printing during the manufacture of the receiving element. 6. A dye-image receiving element according to any one of claims 1 to 4, wherein the black seams are produced during transfer printing of the receiving element. 7. Dye-image receiving element according to one of claims 1 to 4, wherein the black seams are produced after transfer printing of the receiving element. 8. Dye image receiving element according to one of the preceding claims, wherein the receiving element is provided with a transparent cover layer after transfer printing. 9. Dye-image-receiving element according to claim 8, wherein the cover layer is provided with black seams. 10. A dye thermal transfer printing process for obtaining black and white printed copies of images for medical diagnostics, in which a black dye donor element comprising a support and thereon a dye layer to which the Dye-receiving layer of a receiving element as defined in any preceding claim, so that their surfaces touch, is heated imagewise.